The present invention is related generally to radio communication devices. More particularly, the present invention relates to a method and apparatus for distributing processing load among a group of local radios when receiving radio frequency transmissions from a remote radio.
Radio communication systems have been developed which provide two-way radio communication of voice and data between a mobile station and fixed base stations of the system. Using a mobile station in such a system, a subscriber can initiate calls and receive calls while located in the service area adjacent one or more base stations of the system. The service area may extend a distance of 50 km or more from the base station and transmissions within the system, both from the base station and from mobile stations, are relatively high power. By a process of registration, the system maintains location information for the mobile station so that pages may be sent to alert the mobile station.
To enhance user convenience, mobile stations are portable. The mobile station may register with any base station in the system when transported in the vicinity of the base station. Ongoing radio communication with a given mobile station may be handed off among base stations to provide full mobility within the system. Examples of such systems include cellular telephone systems and trunked radio systems.
To further enhance user convenience, mobile stations are conventionally powered by a depletable energy source such as a battery. Battery power provides true portability for a limited period of time while the battery retains sufficient charge to operate the mobile station. When operated under battery power, the user of the mobile station is free to move about the service area of the system but can still initiate and receive calls.
Various techniques have been developed to reduce the power consumption of a mobile station, thereby extending the time between battery recharges. Some of these techniques are implemented at a system level. For example, in some systems, a mobile station is required only to be active only during a time period associated with transmission of a paging channel by base stations of the system. Otherwise, if not actively engaged in a call, the mobile station enters a low-power sleep mode to extend battery life. After the sleep mode, the mobile station regains synchronization with system timing to receive the paging channel, decode the information contained therein and detect a page intended for the mobile station. Other techniques for extending battery life are implemented in the design of an individual mobile station. For example, improved synchronization methods allow extension of the low power sleep mode while ensuring re-synchronization with system timing.
Even with these techniques, a substantial portion of battery life is expended detecting transmissions that might be intended for the mobile station. For example, in some implementations, when searching for a transmission from a base station, the mobile station must power up its analog front end circuit, its microprocessor or other controller and decoding circuitry. This must be done during each possible transmission of paging information, even though a transmission intended for the mobile station is received only rarely. In next generation radio communication systems, the situation is even more severe, since decoding transmissions will require substantial processing power to decode each received instance of a paging channel. This is referred to as joint detection operation.
Accordingly, there is a need for an improved method and apparatus for reducing power consumption in mobile stations of a radio communication system.